storage update

courses/models.py

@@ -158,10 +158,10 @@ class Course(models.Model):
         lessons = self.get_lesson_list()
         try:
             n = lessons[lessons.index(lesson)+1]
-            if f is None or f(lesson):
+            if f is None or f(n):
                 return n
             else:
-                return self.get_next(lesson, f)
+                return self.get_next(n, f)
         except IndexError:
             pass
 
@@ -170,7 +170,7 @@ class Course(models.Model):
         idx = lessons.index(lesson) - 1
         if idx > -1:
             prev = lessons[idx]
-            if f is None or f(lesson):
+            if f is None or f(prev):
                 return prev
             else:
                 return self.get_previous(prev, f)